Here are a number of websites to help you practice your mental math skills. Select a topic/worksheet that aligns with your Summer Homework mental math assignment and then PRACTICE WITHOUT your calculator. Then check your answers with your calculator and find your errors. Get in the habit of SHOWING ALL WORK on paper even though it's only for practice. Establish good habits even when no one is checking!
K-5 Math Worksheets: Fifth Grade Math Worksheets
Common Core Math Sheets: https://commoncoresheets.com/math
Effortless Math: Grade 8 Math Worksheets